Wireless communication method, node, and monitoring node

ABSTRACT

A first node selects a selection node that is the send source of a packet with the highest received radio wave intensity from among packets received from a plurality of second node. The first node sends, to the selection node, a report packet that stores therein an identifier that specifies each of a plurality of first nodes and whose destination is a third node. The second node adds an identifier that specifies each of the plurality of second nodes to the report packet that was received from the first node with the received radio wave intensity that is equal to or greater than a predetermined value among the report packets which are transmitted by the plurality of first nodes and relays the report packet to the third node. The third node detects a node corresponding to the identifier that is not included in the report packets received.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No.PCT/JP2012/058753, filed on Mar. 30, 2012 and designating the U.S., theentire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are directed to a wirelesscommunication method, a node, and a monitoring node.

BACKGROUND

In recent years, wireless ad hoc networks in which terminals aredirectly connected without using network infrastructure, such as accesspoints, are used. Nodes constituting a wireless ad hoc networkautonomously construct paths by exchanging message referred to as, forexample, HELLO packets with neighboring nodes. Accordingly, each of thenodes can deliver data to a target destination node via another node byautonomously detouring a node in which a failure has occurred.

There is a known method, as a method of managing each of the nodes thatconstituting a wireless ad hoc network, of calculating the relativedistance from a fixed node that participates in a network and managingthe location of each of the nodes. Furthermore, there is a known methodof providing each node with a global positioning system (GPS) andmanaging the location of the node by using the GPS.

-   Patent Document 1: Japanese National Publication of International    Patent Application No. 2005-526444-   Patent Document 2: Japanese Laid-open Patent Publication No.    2011-048493

However, in a system in which a path change is frequently occurs due tothe moving of each node, even if the conventional technology is used,there is a problem in that it is not possible to specify the location ofa node that is separated from a wireless ad hoc network.

For example, in the method of calculating the relative distance, becausethe location of a node is specified at the relative distance from afixed node, it is difficult to specify the location of each node in asystem in which no fixed node is present. Furthermore, in a system inwhich a node may sometimes be moved inside a building or moved to abasement, even if the GPS is used, it is not possible to accuratelymeasure the location of the node. Consequently, in the method that usesthe GPS, it is difficult to specify the location in which a node isseparated.

SUMMARY

According to an aspect of the embodiment, a wireless communicationmethod is used in a wireless system including a plurality of firstnodes, a plurality of second nodes and a third node which execute awireless communication using a wireless ad hoc network. the wirelesscommunication method includes selecting a selection node that is a sendsource of a packet with the highest received radio wave intensity fromamong packets which are transmitted by the plurality of second nodes, bythe plurality of first nodes; sending, to the selection node, a reportpacket that includes an identifier that specifies each of the pluralityof first nodes and whose destination is the third node, by the pluralityof first nodes; adding an identifier that specifies each of theplurality of second nodes to the report packet which is received withthe received radio wave intensity that is equal to or greater than apredetermined value among the report packets which are transmitted bythe plurality of first nodes and relaying the report packet to the thirdnode, by the plurality of second nodes; and detecting a nodecorresponding to the identifier that is not included in the reportpackets received from the plurality of second nodes, by the third node.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating an example of the overallconfiguration of a wireless ad hoc network according to a firstembodiment;

FIG. 2 is a functional block diagram illustrating the configuration of anode;

FIG. 3 is a schematic diagram illustrating an example of informationstored in a link table of nodes;

FIG. 4 is a schematic diagram illustrating an example of informationstored in a path table of nodes;

FIG. 5 is a functional block diagram illustrating the configuration of amonitoring node;

FIG. 6 is a schematic diagram illustrating an example of informationstored in a link table of a monitoring node;

FIG. 7 is a schematic diagram illustrating an example of informationstored in a path table of monitoring nodes;

FIG. 8 is a flowchart illustrating the flow of a process performedbetween when a HELLO packet is received and when a report packet issent;

FIG. 9 is a flowchart illustrating the flow of a report packet relayingprocess;

FIG. 10 is a flowchart illustrating the flow of a separation nodedetecting process;

FIG. 11 is a schematic diagram illustrating a specific example of theoccurrence of a separation node;

FIG. 12 is a schematic diagram illustrating an example of the topology;

FIG. 13 is a schematic diagram illustrating an example of a list;

FIG. 14 is a sequence diagram illustrating the flow of a process thatadds path information to a report packet and sends the packet;

FIG. 15 is a flowchart illustrating the flow of a process of reducingthe number of packets by diverting a report packet; and

FIG. 16 is a block diagram illustrating an example of the hardwareconfiguration of a node.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be explained withreference to accompanying drawings. The present invention is not limitedto these embodiments.

[a] First Embodiment

Overall Configuration

FIG. 1 is a schematic diagram illustrating an example of the overallconfiguration of a wireless ad hoc network according to a firstembodiment. As illustrated in FIG. 1, the system in the wireless ad hocnetwork is constituted by multiple nodes 10 and a monitoring node 50.The number of nodes illustrated in FIG. 1 is only an example and is notlimited thereto.

In this example, It is assumed that a children observation system thatmonitors a group behavior of children and that detects a child who islikely to separate from the group. Specifically, a leader, such as aparent, corresponds to a monitoring node and each of the childrencorresponds to each node. In other words, the system illustrated in FIG.1 is a system in which a path change is frequently occurs due to themoving of each of the nodes.

Furthermore, each of the nodes illustrated in FIG. 1 sends and receivesa regular message called, for example, a HELLO packet to and from aneighboring node and then creates path information. Specifically, themonitoring node 50 exchanges, with a node A, a HELLO packet thatincludes path information that is stored with each other. The node Aexchanges, with the monitoring node 50, a node B, and a node C, a HELLOpacket that includes therein path information that is stored with eachother. The node B exchanges, with the node A, a HELLO packet thatincludes path information that is stored with each other. The node Cexchanges, with the node A, a HELLO packet that includes therein pathinformation that is stored with each other.

In this system, the node A is located in a single hop from themonitoring node 50 and directly sends data to the monitoring node 50.The node B is located in two hops from the monitoring node 50 and sendsdata to the monitoring node 50 via the node A. Similarly, the node C islocated in two hops from the monitoring node 50 and sends data to themonitoring node 50 via the node A. Specifically, the node A is a relaynode and the node B and the node C are end nodes.

In this state, the node B or the node C selects, from among the packetsreceived from neighboring nodes, the node A as the send source of thepacket with the highest received radio wave intensity. Then, the node Bor the node C sends, to the selected node A, a report packet in which anidentifier that specifies its own node is included and the monitoringnode 50 is indicated as the destination. The node A adds the identifierof its own node to the report packet that has a received radio waveintensity that is equal to or greater than a predetermined value andthat is received from the node B or the node C and then relays thereport packet to the monitoring node 50. The monitoring node detects anode that is not included in the report packet received from the node A.

Specifically, while each of the nodes 10 adds information on its ownnode to a report packet, each of the nodes 10 selects a node with alarge received signal strength indicator (RSSI) value and then relaysthe report packet to the monitoring node 50. Furthermore, even if eachof the nodes 10 receives a report packet, each of the nodes 10 discardsa report packet with an RSSI value that is smaller than thepredetermined value. Then, the monitoring node 50 detects a node thatdisappeared from the report packet. Consequently, even if no fixed nodeor no GPS is specified, by using an ad hoc network function, it ispossible to detect a node that is likely to separate from the network ordetect the location of that node.

Configuration of a Node

FIG. 2 is a functional block diagram illustrating the configuration of anode. Because the node A, the node B, and the node C illustrated in FIG.1 have the same configuration, descriptions thereof will be given as thenode 10.

As illustrated in FIG. 2, the node 10 includes a wireless interface unit11, an ad hoc protocol processing unit 12, a link table 13, a path table14, a data receiving processing unit 15, a data processing unit 16, anda data sending processing unit 17.

The wireless interface unit 11 is a wireless communication interfacethat performs wireless communication with another node. For example, thewireless interface unit 11 receives, from a neighboring node, a HELLOpacket, a report packet, or the like, and then outputs the packet to thead hoc protocol processing unit 12. Furthermore, the wireless interfaceunit 11 broadcasts a HELLO packet received from the ad hoc protocolprocessing unit 12 to neighboring nodes or sends, to the destinationnode, the report packet received from the ad hoc protocol processingunit 12.

The ad hoc protocol processing unit 12 adds an ad hoc header to eachpacket sent from the data sending processing unit 17, sends the eachpacket to the destination, and outputs the packet received by thewireless interface unit 11 to the data receiving processing unit 15. Forexample, if a HELLO packet is input from the data sending processingunit 17, the ad hoc protocol processing unit 12 adds an ad hoc header tothe HELLO packet and then broadcasts the packet to the neighboringnodes. Furthermore, if a report packet is input from the data sendingprocessing unit 17, the ad hoc protocol processing unit 12 adds an adhoc header to the report packet and sends the report packet to thedestination node.

The ad hoc protocol processing unit 12 includes a packet filtering unit12 a. The packet filtering unit 12 a is a processing unit that performsfiltering of a packet by using the received radio wave intensity.Specifically, if the packet filtering unit 12 a receives a HELLO packetor a report packet, the packet filtering unit 12 a measures an RSSIvalue obtained the packet is received. Then, the packet filtering unit12 a outputs, to the data receiving processing unit 15, a packet inwhich the received RSSI value is greater than a predetermined threshold.Furthermore, for the packet in which the RSSI value obtained at thereception of the packet is smaller than the predetermined threshold, thepacket filtering unit 12 a may discard the packet or may output thepacket to the data receiving processing unit 15 together with anotification indicating that the packet is out of the processing target.

The link table 13 is a storing unit that stores therein information onneighboring nodes. The information stored in the link table 13 isinformation that is extracted by the data receiving processing unit 15from a HELLO packet. Accordingly, the link table 13 is updated everytime a HELLO packet is received. Furthermore, it is assumed that thelink table 13 according to the first embodiment is created on the basisof a HELLO packet that is received with an RSSI value that is equal toor greater than a predetermined value. Accordingly, if no HELLO packetthat is received with an RSSI value that is equal to or greater than apredetermined value is present, there may be a case in which the linktable 13 is empty.

FIG. 3 is a schematic diagram illustrating an example of informationstored in a link table of nodes. As illustrated in FIG. 3, the linktable 13 stores therein, for example, the “local send source address(LS), the RSSI value, the HELLO reception count, the HELLO requestinterval, and the access key”. The information illustrated in FIG. 3 isonly an example; therefore, the information may also arbitrarily bechanged by adding, for example, quality information indicating thequality between links.

The “local send source address (LS)” is address information on the sendsource node of the received HELLO packet. The “RSSI value” is thereceived radio wave intensity at the time when a HELLO packet isreceived. The “HELLO reception count” indicates the number of times theHELLO packets received from the local send source (LS). The “HELLOrequest interval” indicates the interval of sending and receiving apacket with the LS. The “access key” indicates an encryption key that isused when the frame type sent from a send source node decodes anencryption of a data frame that is other than the HELLO packet.

In the example illustrated in FIG. 3, the node 10 corresponds to thenode C illustrated in FIG. 1. In FIG. 3, the symbol of AAA is specifiedas an access key to the node A. Furthermore, the interval at which aHELLO packet is received from the node A is one second and a HELLOpacket is received five times before now. Furthermore, FIG. 3 indicatesthat the latest HELLO packet was received with the RSSI value of 80.

The path table 14 stores therein routing information on a path to thedestination node. Specifically, from among multiple paths to thedestination node, the path table 14 stores therein a predeterminednumber of paths as appropriate paths in the order of, for example, goodquality. Because the path table 14 is created on the basis of the linktable 13, if the link table 13 is empty, there may be a case in whichthe path table 14 is also empty. FIG. 4 is a schematic diagramillustrating an example of information stored in a path table of nodes.As illustrated in FIG. 4, the path table 14 stores therein, in anassociated manner, the “global destination (GD), the local destination(LD), the hop count, and the quality”.

The “GD” stored in the path table 14 indicates a global destinationaddress and is address information on the last destination node. The“LD” is address information on a relay destination node that is thesubsequent destination and that is used to deliver a packet to a GD. The“hop count” indicates a hop count to a GD. The “quality” indicates thequality of a path to a GD and is obtained by converting, for example, anamount of delay, the radio wave intensity, the packet loss rate, or thelike into numbers. In this example, the quality is higher as a value isgreater.

The example illustrated in FIG. 4 indicates a case in which the node 10is the node C illustrated in FIG. 1. FIG. 4 indicates that the node Chas two paths that are used to send a packet to the monitoring node 50.A first path is a two-hop path that goes through the node A and a secondpath is a three-hop path that goes through the node B. Between these twopaths, the node C selects the path that goes through the node A, whosequality is better than the node B, and sends the packet to themonitoring node.

A description will be given here by referring back to FIG. 2. The datareceiving processing unit 15 is a processing unit that includes a HELLOprocessing unit 15 a and a radio wave selecting unit 15 b and thatperforms a receiving process on data that is input from the ad hocprotocol processing unit 12.

The HELLO processing unit 15 a is a processing unit that updates thepath table 14 and the link table 13 on the basis of the HELLO packetreceived with an RSSI value that is equal to or greater than thepredetermined value. For example, the HELLO processing unit 15 areceives, from the packet filtering unit 12 a, a HELLO packet and anRSSI value at the time when the HELLO packet is received. Then, theHELLO processing unit 15 a extracts, from the HELLO packet, the LS, thequality, the hop count to the monitoring node, and the like.Subsequently, the HELLO processing unit 15 a updates the “RSSI value”that is associated with the extracted LS and that is stored in the linktable 13 to the value at the time when the HELLO packet is received thistime and then increments the “HELLO reception count”. If the extractedLS is not stored in the link table 13, the HELLO processing unit 15 acreates a new record.

Furthermore, the HELLO processing unit 15 a updates the path table 14 onthe basis of the link table 13. For example, the HELLO processing unit15 a creates, in the path table 14, a table in which the LS stored inthe link table 13 is set to the LD and the GD is set to the monitoringnode 50. Then, the HELLO processing unit 15 a increments the hop countextracted from the HELLO packet in which the LS is set to the sendsource and then stores the incremented value as a hop count in theassociated table in the path table 14. At this point, if multiple hopcounts are included in a HELLO packet, the HELLO processing unit 15 aincrements the smallest value. Furthermore, the HELLO processing unit 15a extracts the quality from a HELLO packet in which the LS is set to thesend source and then the quality in the associated table in the pathtable 14.

The radio wave selecting unit 15 b is a processing unit that controlssuch that a path with the highest RSSI value is selected. For example,the radio wave selecting unit 15 b refers to the link table 13 and sortsthe records in descending order of the RSSI values such that the recordwith the highest RSSI value from among the records is the top in thelink table 13.

The data processing unit 16 is a processing unit that includes a HELLOpacket creating unit 16 a, a report packet creating unit 16 b, and areport packet relaying unit 16 c and that creates and relays variouspackets by using these units in the data processing unit 16.

The HELLO packet creating unit 16 a is a processing unit that creates aHELLO packet at predetermined intervals. Specifically, the HELLO packetcreating unit 16 a creates a HELLO packet to which path informationstored in the path table 14, a hop count to the monitoring node 50, andthe like is added and then outputs the created HELLO packet to the datasending processing unit 17. For example, the HELLO packet creating unit16 a inserts the pieces of path information stored in the path table 14into a HELLO header. Specifically, the HELLO packet creating unit 16 acreates HELLO headers, the number of which is the same as that ofrecords present in the path table 14. Then, the HELLO packet creatingunit 16 a creates HELLO packets each of which includes the created HELLOheader.

The report packet creating unit 16 b is a processing unit that creates areport packet that notifies the presence of its own node. Specifically,the report packet creating unit 16 b creates a report packet by addingan identifier that indicates a report packet or an identifier thatspecifies its own node to a packet that has been sent and received in atypical ad hoc network. Then, the report packet creating unit 16 boutputs the created report packet to the data sending processing unit17. Any timing is available for the timing at which the report packet iscreated. Furthermore, the timing may also be synchronized with thenodes, or the timing may also be specified by the monitoring node 50.

The report packet relaying unit 16 c is a processing unit that relays,to the monitoring node 50, a report packet that has been received withthe RSSI value that is equal to or greater than the predetermined value.Specifically, from among the report packets sent from the other nodes,the report packet relaying unit 16 c receives a report packet with theRSSI value that is equal to or greater than the predetermined value fromthe packet filtering unit 12 a. Then, the report packet relaying unit 16c adds an identifier that is used to identify its own node to thereceived report packet and then outputs the report packet to the datasending processing unit 17.

For example, if the node 10 is the node A, the report packet relayingunit 16 c adds an identifier of the node A to the report packet receivedfrom the node 8 at the position after the identifier of the node B thathas already been added and then relays the packet to the monitoring node50. Similarly, the report packet relaying unit 16 c adds an identifierof the node A to the report packet received from the node C at theposition after the identifier of the node C that has already been addedand then relays the packet to the monitoring node 50.

The data sending processing unit 17 is a processing unit that performs aprocess of sending a HELLO packet or a report packet. For example, whena HELLO packet is input from the HELLO packet creating unit 16 a, thedata sending processing unit 17 specifies that the destination indicatesbroadcast addresses. Then, the data sending processing unit 17 outputsthe HELLO packet and the destination to the ad hoc protocol processingunit 12.

Furthermore, when a report packet is input from the report packetcreating unit 16 b, the data sending processing unit 17 specifies thatthe destination (GD) is the monitoring node 50. Subsequently, the datasending processing unit 17 refers to the path table 14 and specifiesthat there are two paths toward the monitoring node and that thesubsequent destination (LD) is the node A or the node B. Then, the datasending processing unit 17 refers to the link table 13 and selects,between the node A and the node B, the node A that has the higher RSSIvalue. Then, the data sending processing unit 17 outputs, to the ad hocprotocol processing unit 12, the report packet and an instructionindicating that transmission is performed by using the node A as the LD.If the data sending processing unit 17 receives an input of the reportpacket from the report packet relaying unit 16 c, the data sendingprocessing unit 17 performs the same process as that described above.

Furthermore, when the ad hoc protocol processing unit 12 sends eachpacket, the ad hoc protocol processing unit 12 rewrites the Local Source(LS) stored in each packet to its own node. As described above, when thedata sending processing unit 17 sends a HELLO packet or a report packet,the data sending processing unit 17 refers to the link table 13 or thepath table 14 and specifies a destination address or the like.Consequently, if no entry is present in a table, the data sendingprocessing unit 17 is not able to send a packet.

Configuration of the Monitoring Node

FIG. 5 is a functional block diagram illustrating the configuration of amonitoring node. As illustrated in FIG. 5, the monitoring node 50includes a wireless interface unit 51, an ad hoc protocol processingunit 52, a link table 53, a path table 54, a data receiving processingunit 55, a data processing unit 56, and a data sending processing unit57.

The wireless interface unit 51 is a wireless communication interfacethat performs wireless communication with the other nodes. For example,the wireless interface unit 51 receives a HELLO packet, a report packet,or the like from a neighboring node and then outputs the packet to thead hoc protocol processing unit 52. Furthermore, the wireless interfaceunit 51 broadcasts a HELLO packet received from the ad hoc protocolprocessing unit 52 to neighboring nodes or sends a report packetreceived from the ad hoc protocol processing unit 52 to a destinationnode.

The ad hoc protocol processing unit 52 adds an ad hoc header to each ofthe packets sent from the data sending processing unit 57, sends thepackets to each destination, and outputs the packet received by thewireless interface unit 51 to the data receiving processing unit 55. Theprocess performed by the ad hoc protocol processing unit 52 is the sameas that performed by the ad hoc protocol processing unit 12; therefore,a description thereof in detail will be omitted. The ad hoc protocolprocessing unit 52 includes a packet filtering unit 52 a; however, theprocess performed by the packet filtering unit 52 a is the same as thatperformed by the packet filtering unit 12 a; therefore, a descriptionthereof in detail will be omitted.

The link table 53 is a storing unit that stores therein information on aneighboring node. The information stored in the link table 53 isinformation that is extracted by the data receiving processing unit 55from a HELLO packet. Accordingly, the link table 53 is updated everytime a HELLO packet is received. Furthermore, it is assumed that thelink table 53 according to the first embodiment is created on the basisof a HELLO packet that has been received with an RSSI value that isequal to or greater than a predetermined value.

FIG. 6 is a schematic diagram illustrating an example of informationstored in a link table of a monitoring node. As illustrated in FIG. 6,the link table 53 stores therein, for example, the “local send sourceaddress (LS), the RSSI value, the HELLO reception count, the HELLOrequest interval, and the access key”. The pieces of information storedin the link table 53 are the same as those illustrated in FIG. 3;therefore, descriptions thereof in detail will be omitted.

In the example illustrated in FIG. 6, the symbol of AAA is specified asan access key to the node A. Furthermore, the interval at which a HELLOpacket is received from the node A is one second and a HELLO packet isreceived five times before now. Furthermore, FIG. 6 indicates that thelatest HELLO packet has been received with the RSSI value of 80.

The path table 54 stores therein routing information on a path to thedestination node. Specifically, from among multiple paths to thedestination node, the path table 54 stores therein, in the order of, forexample, good quality, the predetermined number of paths as appropriatepaths. FIG. 7 is a schematic diagram illustrating an example ofinformation stored in a path table of monitoring nodes. As illustratedin FIG. 7, the path table 54 stores therein, in an associated manner,the “GD, the LD, the hop count, and the quality”. The pieces ofinformation stored in the path table 54 are the same as thoseillustrated in FIG. 4; therefore, descriptions thereof in detail will beomitted.

The example illustrated in FIG. 7 indicates that the monitoring node haspaths to the node A, the node B, and the node C that are used as thedestination. The path to the node A is a 1-hop path to the node A thatcorresponds to both the destination and the relay destination and hasthe quality of 70. The path to the node B is a 2-hop path to the node Athat corresponds to the relay destination and has the quality of 50. Thepath to the node C is a 2-hop path to the node A that corresponds to therelay destination and has the quality of 30.

A description will be given here by referring back to data FIG. 5. Thedata receiving processing unit 55 is a processing unit that includes aHELLO processing unit 55 a and a radio wave selecting unit 55 b and thatperforms a receiving process on data that is input from the ad hocprotocol processing unit 52. Because the data receiving processing unit55 performs the same process as that performed by the data receivingprocessing unit 15, the HELLO processing unit 55 a performs the sameprocess as that performed by the HELLO processing unit 15 a, and theradio wave selecting unit 55 b performs the same process as thatperformed by the radio wave selecting unit 15 b described the above byreferring to FIG. 2, descriptions thereof in detail will be omitted.

The data processing unit 56 is a processing unit that includes a HELLOpacket creating unit 56 a and a separation detecting unit 56 b and thatcreates and relays various packets by using these units included in thedata processing unit 56. If a power supply of each of the nodes isturned on and an ad hoc network is constructed, the data processing unit56 notifies all of the nodes of the transmission timing of a reportpacket. The transmission timing can arbitrarily be set, such as aninterval of three seconds. The HELLO packet creating unit 56 a performsthe same process as that performed by the HELLO packet creating unit 16a described above by referring to FIG. 2; therefore, a descriptionthereof in detail will be omitted.

The separation detecting unit 56 b is a processing unit that detects anode that has been separated from or that is likely to be separated froman ad hoc network. Specifically, the separation detecting unit 56 bcompares information on a node that is extracted from a report packetthat was received in the past with information on a node that isextracted from a report packet that is received this time and thenspecifies a node that is not able to be extracted this time as aseparation prediction node.

For example, it is assumed that the separation detecting unit 56 b hasreceived the report packet A, the report packet B, and the report packetC from the node A at the immediately previous timing. Then, theseparation detecting unit 56 b extracts the identifier A of the node Afrom the report packet A. Accordingly, the separation detecting unit 56b recognizes that the report packet A is sent from the node A.Furthermore, the separation detecting unit 56 b sequentially extractsthe identifier B of the node B and the identifier A of the node A, inthis order, from the report packet B. Accordingly, the separationdetecting unit 56 b recognizes that the report packet B is sent startingfrom the node B via the node A. Furthermore, the separation detectingunit 56 b sequentially extracts the identifier C of the node C and theidentifier A of the node A, in this order, from the report packet C.Accordingly, the separation detecting unit 56 b recognizes that thereport packet C is sent starting from the node C via the node A.Consequently, the separation detecting unit 56 b can recognize that thenode A is located in one hop from the monitoring node 50 and recognizethat the node B and the node C are located in one hop from the node A.

Thereafter, it is assumed that the separation detecting unit 56 breceives, at this timing, the report packet A and the report packet Bfrom the node A. Then, the separation detecting unit 56 b extracts theidentifier A of the node A from the report packet A. Accordingly, theseparation detecting unit 56 b recognizes that the report packet A issent from the node A. Furthermore, the separation detecting unit 56 bsequentially extracts the identifier B of the node B and the identifierA of the node A, in this order, from the report packet B. Thus, theseparation detecting unit 56 b recognizes that the report packet B issent starting from the node B via the node A. Consequently, theseparation detecting unit 56 b can recognize that the node A is locatedin one hop from the monitoring node 50 and recognize that the node B islocated in one hop from the node A.

Because the node C is not detected from the extraction result performedimmediately previously and performed this time, the separation detectingunit 56 b specifies the node C as a separation prediction node that islikely to separate. The reason that the separation detecting unit 56 bdetects the node C as a separation prediction node is that severalreasons for the node C not sending a report packet can be conceivable.It is conceivable, as the reason for this, that the node has failed or areport packet can be received from the node C but the packet isdiscarded due to a small RSSI value. For another reason, it isconceivable that the node C is not able to receive a HELLO packet from aneighboring node because, for example, the node C is away from the othernode or enters inside a building or it is conceivable that, even if thenode C can receive a HELLO packet from a neighboring node, the RSSIvalue is small. In such a case, the node C is not able to send a HELLOpacket because an entry is deleted from the link table 53 or the pathtable 54.

As described above, because several reasons can be conceived, theseparation detecting unit 56 b determines that the node C is likely toseparate from the network. Furthermore, the separation detecting unit 56b can create the topology on the basis of the identifier of the nodeextracted from the report packet and on the basis of the order of theidentifiers stored in the report packet. Consequently, the separationdetecting unit 56 b can perform warning by displaying, on the topology,an alarm at the position in which the node C immediately previously isconnected. Furthermore, because the separation detecting unit 56 b canspecify that the node to which the node C immediately previously isconnected is the node B, a warning message can be sent to the node C viathe node B. Furthermore, the separation detecting unit 56 b may alsodisplay the created topology on a displaying unit or the like.Alternatively, the separation detecting unit 56 b may also send thecreated topology to a management server or the like connected in anetwork. Furthermore, the information that has been received andextracted by the separation detecting unit 56 b may also be sent to amanagement server and then the management server may perform separationdetection or topology creation.

The data sending processing unit 57 is a processing unit that performs aprocess of sending a HELLO packet or a report packet. The data sendingprocessing unit 57 performs the same process as that performed by thedata sending processing unit 17 described by referring to FIG. 2;therefore, a description thereof in detail will be omitted. Furthermore,similarly, the data sending processing unit 57 can also perform theprocess on the warning message described above.

Flow of Processes

In the following, the flow of a process performed by each of the nodesor the monitoring node will be described. Specifically, a descriptionwill be given of a report packet sending process, a report packetrelaying process, and a separation node detecting process.

Report Packet Sending Process

FIG. 8 is a flowchart illustrating the flow of a process performedbetween when a HELLO packet is received and when a report packet issent. In the following, a description will be given of the flow of theseries of the processes performed between when a HELLO packet isreceived and when a report packet is sent; however, the processes arenot limited thereto. For example, the processes may also be performed atdifferent timing.

As illustrated in FIG. 8, if it is the time to send a HELLO packet (Yesat Step S101), the HELLO packet creating unit 16 a in the node 10creates a HELLO packet (Step S102). Then, the data sending processingunit 17 broadcasts the HELLO packet to the neighboring nodes (StepS103).

Then, when the packet filtering unit 12 a receives the HELLO packets(Yes at Step S104), the packet filtering unit 12 a discards, from amongthe received HELLO packets, the HELLO packet with the RSSI value that isless than the predetermined value (Step S105).

Subsequently, the HELLO processing unit 15 a updates the link table 13or the path table 14 on the basis of the HELLO packet and then the radiowave selecting unit 15 b sorts the entries in the link table 13 indescending order of the RSSI values (Step S106).

Thereafter, if it is the time to send a report packet (Yes at StepS107), the report packet creating unit 16 b creates a report packet thatincludes the node ID that is used to identify its own node (Step S108).Then, from among the LDs that are related to paths to the monitoringnode 50 that is the destination in the link table 13, the report packetcreating unit 16 b sends a report packet toward the monitoring node 50by using the LD with the highest RSSI value as the subsequentdestination (Step S109). Specifically, the data sending processing unit17 sends a report packet via the ad hoc protocol processing unit 12 andthe wireless interface unit 11 in accordance with the instruction fromthe report packet creating unit 16 b.

Report Packet Relaying Process

FIG. 9 is a flowchart illustrating the flow of a report packet relayingprocess. As illustrated in FIG. 9, when the packet filtering unit 12 areceives report packets from the other node (Yes at Step S201), thepacket filtering unit 12 a discards the report packet with the RSSIvalue that is less than the predetermined value at the time when thepacket is received (Step S202).

Then, the report packet relaying unit 16 c determines whether a reportpacket still remains after the filtering is performed (Step S203).Specifically, the report packet relaying unit 16 c determines whether areport packet that is output from the packet filtering unit 12 a andthat is input via the data receiving processing unit 15 is present.

If the report packet relaying unit 16 c determines that a report packetremains (Yes at Step S203), the report packet relaying unit 16 c addsthe node ID of its own node to the report packet (Step S204). At thispoint, the report packet relaying unit 16 c adds the node ID in theorder of the nodes such that the nodes through which the report packetgoes can be specified.

Then, the report packet relaying unit 16 c uses, from among the LDs thatare related to paths to the monitoring node 50 that is the destinationin the link table 13, the LD with the highest RSSI value as thesubsequent destination and then sends the report packet to themonitoring node 50 (Step S205). Specifically, the data sendingprocessing unit 17 sends a packet via the ad hoc protocol processingunit 12 and the wireless interface unit 11 in accordance with aninstruction from the report packet creating unit 16 b. Furthermore, ifthe report packet relaying unit 16 c determines that no report packetremains (No Step S203), the report packet relaying unit 16 c ends theprocess.

Separation Node Detecting Process

FIG. 10 is a flowchart illustrating the flow of a separation nodedetecting process. As illustrated in FIG. 10, when the packet filteringunit 52 a in the monitoring node 50 receives a report packet from eachnode 10 (Yes at Step S301), the packet filtering unit 52 a discards thereport packet with the RSSI value that is less than the predeterminedvalue at the time when the packet is received (Step S302).

Subsequently, the separation detecting unit 56 b calculates a differencebetween the number of remaining report packets after the filtering andthe number of report packets that are immediately previously received(Step S303). It is assumed that the separation detecting unit 56 bstores the report packet that was immediately previously received or thenumber of report packets in a memory or the like.

Then, if the separation detecting unit 56 b determines that there is nodifference between the number of remaining report packets after thefiltering and the number of report packets that are immediatelypreviously received (No at Step S304), the separation detecting unit 56b ends the process. Specifically, if the separation detecting unit 56 bcan receive the report packets the number of which is the same as thatimmediately previously received, the separation detecting unit 56 bdetermines that no node that is likely to separate is present.

In contrast, if the separation detecting unit 56 b determines that thereis a difference between the number of remaining report packets after thefiltering and the number of report packets that are immediatelypreviously received (Yes at Step S304), the separation detecting unit 56b performs the process at Step S305. In this example, it is assumed thatthe number of report packets that are immediately previously received isgreater than the number of report packets that are received this time.In such a case, the separation detecting unit 56 b specifies a reportpacket that is included in only the immediately previous packets (StepS305). Furthermore, if the number of report packets that are receivedthis time is greater than that immediately previously received, theseparation detecting unit 56 b detects that a new node has joined in thead hoc network.

Then, the separation detecting unit 56 b specifies the send source nodeof the specified report packet, i.e., a creation source node of thereport packet, that is only included in the immediately previouspackets, and then determines that the specified node is the separationprediction node (Step S306).

Furthermore, from the specified report packet that is only included inimmediately previous packets, the separation detecting unit 56 bsequentially extracts the node IDs in the order they are added (StepS307). Then, by combining the extracted node IDs, the separationdetecting unit 56 b specifies the send source node, i.e., the node towhich a separation prediction node is connected immediately before theseparation (Step S308).

Then, the separation detecting unit 56 b extracts the node ID from eachof the report packets that are received this time and combines theextracted node IDs, whereby the separation detecting unit 56 b creates atopology of the ad hoc network (Step S309). Furthermore, the separationdetecting unit 56 b may also use the report packets that are immediatelypreviously received. Furthermore, the separation detecting unit 56 b mayalso display an alarm on the topology such that a separation predictionnode can be identified.

Specific Example

In the following, a description will be given of a specific example inwhich a separation node occurs. FIG. 11 is a schematic diagramillustrating a specific example of the occurrence of a separation node.As illustrated in FIG. 11, it is assumed that the configuration of thead hoc network is the same as that illustrated in FIG. 1. In thisexample, a description will be given of a case in which the node C movesfrom a node C1 that is the neighboring node of the node A to the node C2that is the neighboring node of the node B, then finally moves to thelocation of the node C3, and separates from the network.

If the node C is located at the location of a node C1, because the RSSIvalue of the HELLO packet received from the node A is the greatest, thenode C sends a report packet to the monitoring node 50 via the node A.

Thereafter, when the node C moves to the location of a node C2 and thusis closer to the node B, the RSSI value of the HELLO packet receivedfrom the node A becomes small in the node C, whereas the RSSI value ofthe HELLO packet received from the node B becomes large. Then, becausethe RSSI value of the HELLO packet received from the node B is thelargest, the node C switches the paths to the path via the node B andsends the report packet to the monitoring node 50. At this point, inorder to reduce the variation, a constant hysteresis may also be used.

Furthermore, when the node C moves to the location of a node C3, theRSSI value of the HELLO packet received from the node B becomes small inthe node C. Then, the RSSI value of the HELLO packet received from thenode B is less than the predetermined value in the node C and thus thenode C deletes the node B from the link table 13 or the like.Consequently, the node C stop sending the report packet and thus themonitoring node 50 is not able to receive the report packet from thenode C.

Accordingly, the monitoring node 50 receives, via the node B and thenode A, the report packet sent from the node C until immediatelyprevious time; however, the monitoring node 50 is not able to receivethe report packet this time. Because of this, the monitoring node 50calculates a difference between the number of report packets obtainedimmediately previous time and the number of report packets obtained thistime, detects that the monitoring node 50 is not able to receive thereport packet from the node C, and specifies the node C as a separationprediction node. At this point, the monitoring node 50 can specify thatthe node to which the node C immediately previously connects is the nodeB and can also detect that the node C has separated from the network atthe location in the vicinity of the node B.

Furthermore, the monitoring node 50 can also notify an administrator ofa separation prediction node by using a topology or a list. FIG. 12 is aschematic diagram illustrating an example of the topology. FIG. 13 is aschematic diagram illustrating an example of a list. As illustrated inFIG. 12, the monitoring node 50 can create a topology from the node IDincluded in each of the received report packets and the order of thenode IDs. At this point, the monitoring node 50 can also display analarm such that a separation prediction node can be identified.Furthermore, as illustrated in FIG. 13, the monitoring node 50 storestherein a list for managing, for example, a telephone number or an emailaddress of each node and displays an alarm on the list such that aseparation prediction node is identified. In this way, because themonitoring node 50 can output a separation prediction node as an alarmby using various methods, an administrator can promptly detect theseparation prediction node.

Advantage

As in a children observation system, even if a node frequently moves,each node can be monitored without using a special method, such as aGPS. For example, when kindergartners go to and from a kindergarten in agroup or take a walk in a group, a teacher who leads the kindergartnerscan easily specify an object that has separated from a group behavior ina group, in particular, in a moving group, or an object that is likelyto separate from the group and can easily be aware of a person from whomthe object is likely to separate. Consequently, it is possible to reducethe load applied to the leader.

Furthermore, because it is possible to detect a node that is likely toseparate from an ad hoc network, i.e., a node that has a small RSSIvalue but that can receive a packet, it is possible to take an action,such as sending an alarm to the target node before the node actuallyseparates from the network. Consequently, separation can be previouslyprevented. Furthermore, because it is possible to specify the node towhich a separation prediction node is immediately previously connected,a search instruction can be sent to that node indicating the searchingfor the separation prediction node, it is possible to implement earlydetection of a separation prediction node.

Second Embodiment

In the following, an example of sending a report packet by using amethod different from the first embodiment will be described.Specifically, an example in which each node sends a report packet towhich path information that is retained by each node is added and anexample in which each node diverts a report packet from another nodewill be described.

Sending Path Information

In the following, a description will be given of an example in whicheach node adds two pieces of path information that has a higher RSSIvalue and sends a report packet. FIG. 14 is a sequence diagramillustrating the flow of a process that adds path information to areport packet and sends the packet.

As illustrated in FIG. 14, the node C creates, from the link table 13, areport packet (C) to which two pieces of superior link information areadded (Step S401) and sends the report packet (C) to the node A that hasthe highest RSSI value at the time when a HELLO packet is received(Steps S402 and S403). In the second embodiment, a description will begiven of an example of adding two pieces of superior link information;however, the number of additions can be arbitrarily set.

The node A adds the node ID of its own node to the report packet (C)received from the node C and then transfers the report packet (C) to themonitoring node 50 (Step S404 and S405). Then, the monitoring node 50receives, via the node A, the report packet (C) sent from the node C(Step S406).

Furthermore, the node B creates, from the link table 13, a report packet(B) to which two pieces of superior link information are added (StepS407) and sends the report packet (B) to the node A that has the highestRSSI value at the time when a HELLO packet is received (Steps S408 andS409).

The node A adds the node ID of its own node to the report packet (B)received from the node B and transfers the report packet (B) to themonitoring node 50 (Step S410 and S411). Then, the monitoring node 50receives, via the node A, the report packet (B) sent from the node B(Step S412).

Furthermore, the node A creates, from the link table 13, a report packet(A) to which two pieces of superior link information are added (StepS413) and sends the report packet (A) to the monitoring node 50 (StepsS414 and S415). Then, the monitoring node 50 receives the report packet(A) sent from the node A (Step S416).

Then, the separation detecting unit 56 b in the monitoring node 50calculates the distance between the nodes (Step S417), creates atopology in which the distance and the direction are taken intoconsideration, and displays the topology (Step S418). For example, theseparation detecting unit 56 b can estimate the distance from the RSSIvalues and can specify the positional relationship between the nodes onthe basis of information indicating which packet has passed throughwhich node. Furthermore, each of the multiple nodes acquires an RSSIvalue between one of the other nodes and can estimate the location of anode on the basis of the acquired data. For example, if the node Aretains the distance between the node B and the node C and if the node Bretains the distance between the node A and the node C, it is possibleto estimate that the location of the node C is the intersection of acircle of the distance between the node A and the node C and a circle ofthe distance between the node B and the node C. In such a case, thesimilar positional relationships between multiple nodes are acquired andthe least squares method may also be used in order to calculate thelocation of a node on the basis of the acquired positionalrelationships.

For example, it is assumed that the RSSI value at the time of receptionof a report packet whose send source is the node C is 40. Furthermore,it is assumed that the RSSI value at the time of reception of a HELLOpacket sent from the node A included in the report packet is 80 and theRSSI value at the time of reception of a HELLO packet sent from the nodeB included in the report packet is 20. In such a case, the separationdetecting unit 56 b calculates the relative positional relationshipbetween the monitoring node 50 and the node C by using the least squaresmethod using the RSSI value of 40 and the RSSI value of 80. Similarly,the separation detecting unit 56 b calculates the relative positionbetween the monitoring node 50 and the node C by using the least squaresmethod using the RSSI value of 40 and the RSSI value of 20. Then, theseparation detecting unit 56 b specifies the direction of the node Cfrom the calculated both relative position.

By doing so, it is possible to easily be aware of the relative positionfrom a monitoring node that monitors a kindergartner who is likely toseparate from a group and thus the monitoring can be performed with highaccuracy. Furthermore, because it is possible to create a topologytaking into consideration the relative position or the direction, anobserver or a leader can easily identify the location of a node and thuseasily help a separation node.

Relay a Report Packet

FIG. 15 is a flowchart illustrating the flow of a process of reducingthe number of packets by diverting a report packet. As illustrated inFIG. 15, when it is time to determine the role of its own node (StepS501), the report packet creating unit 16 b in the node 10 determineswhether its own node is the end point (Step S502). For example, thereport packet creating unit 16 b determines whether its own node is theend node in an ad hoc network on the basis of whether a report packet isrelayed before now.

If the report packet creating unit 16 b determines that its own node isthe end point (Yes at Step S502), the report packet creating unit 16 bdetermines whether a report packet is to be sent (Step S503). If it isthe time to send a report packet (Yes at Step S503), the report packetcreating unit 16 b creates a report packet in which the node ID thatidentifies its own node is included (Step S504). Then, the report packetcreating unit 16 b sends the report packet toward the monitoring node 50by using, as the subsequent destination, an LD with the highest RSSIvalue from among the LDs related to a path in which the monitoring node50 is the destination in the link table 13 (Step S505). If it is thetime to send a report packet (No at Step S503), the report packetcreating unit 16 b returns to Step S502 and repeats the process at StepS502 and the subsequent processes.

In contrast, if the report packet creating unit 16 b determines that itsown node is not the end point but is a relay node (No at Step S502), thereport packet creating unit 16 b stops creating the report packet (StepS506).

Thereafter, when the report packet relaying unit 16 c receives a reportpacket with a high RSSI value from another node (Yes at Step S507), thereport packet relaying unit 16 c adds the node ID of its own node to thereceived report packet (Step S508). At this point, the report packetrelaying unit 16 c adds the node ID in the order the report packet isreceived such that the nodes through which the report packet goes can beidentified.

Then, the report packet relaying unit 16 c sends the report packettoward the monitoring node 50 by using, as the subsequent destination,the LD with the highest RSSI value in the link table 13 from among theLDs related to the path in which the monitoring node 50 is thedestination (Step S509).

As described above, the report packet received from the other node canbe diverted as the report packet of its own node. Consequently, it ispossible to reduce the number of report packets reported toward themonitoring node in an ad hoc network. Furthermore, in accordance withthe reduction in the number of packets, the occurrence of congestion canbe suppressed and also can be suppressed even if the number of objectsto be monitored is large.

Third Embodiment

The embodiments of the present invention have been described; however,the present invention is not limited to the embodiments described aboveand can be implemented with various kinds of embodiments other than theembodiment described above. Therefore, another embodiment included inthe present invention will be described below as a second embodiment.

Creating Path Information

In the second embodiment, a description has been given of an example inwhich a predetermined pieces of information is acquired from the linktable 13 that is created from a HELLO packet with RSSI value that isequal to or greater than a predetermined value and then the acquiredinformation is added to a report packet; however, the present inventionis not limited thereto. For example, in such a case, an entry to bestored in the link table 13 may also be created from a HELLO packet withan RSSI value that is less than the predetermined value and pathinformation that is added to the report packet may also be specified bytaking into consideration the entry.

Applies to a Service

In the first embodiment described above, a description has been given ofan example of children going to and from school; however, the presentinvention is not limited thereto. For example, the embodiment can beused to support a team of mountain climbers such that a certain distancecan be maintained between the head and the rear end of the team.Furthermore, in a case of grazing livestock or moving livestock fed bynomad in a group, the relative position of a specific object can bepromptly identified and thus it is possible to speed up the collectionof health management information on the livestock or speed up aprevention action based on the collection.

System

Of the processes described in the embodiments, the whole or a part ofthe processes that are mentioned as being automatically performed canalso be manually performed, or the whole or a part of the processes thatare mentioned as being manually performed can also be automaticallyperformed using known methods. Furthermore, the flow of the processes,the control procedures, the specific names, and the informationcontaining various kinds of data or parameters indicated in the abovespecification and drawings can be arbitrarily changed unless otherwisestated.

The components of each unit illustrated in the drawings are only forconceptually illustrating the functions thereof and are not alwaysphysically configured as illustrated in the drawings. In other words,the specific shape of a separate or integrated device is not limited tothe drawings. Specifically, all or part of the device can be configuredby functionally or physically separating or integrating any of the unitsdepending on various loads or use conditions. Furthermore, all or anypart of the processing functions performed by each device can beimplemented by a CPU and by programs analyzed and executed by the CPU orimplemented as hardware by wired logic.

Hardware Configuration

FIG. 16 is a block diagram illustrating an example of the hardwareconfiguration of a node. Because the nodes and the monitoring node havethe same configuration, a description will be given of a node 100. Asillustrated in FIG. 16, the node 100 includes a communication controlunit 100 a, a physical layer (PHY) 100 b, a bus interface unit 100 c, amemory 100 d, and a central processing unit (CPU) 100 e.

The communication control unit 100 a is a processing unit that performscommunication with another node and is, for example, an antenna or anetwork interface card. The PHY 100 b is a physical layer hardware unit.In the PHY 100 b, an operation related to network connection or datatransmission in the physical layer is stipulated. The PHY 100 bimplements communication with a counterpart device via the communicationcontrol unit 100 a. Furthermore, the PHY 100 b may also be implementedby software.

The bus interface unit 100 c is a bus interface that is used to exchangea signal among a CPU 10 e, the memory 100 d, the PHY 100 b, and thelike. The memory 100 d includes, for example, a read only member (ROM),a random access memory (RAM), or the like and is a storage device thatstores therein a program that implements various processes used in thecommunication method according to the embodiment; a path table and thelink table, which have been described above; and data that is obtainedin the course of a process.

The CPU 100 e is a processing unit that manages various processesperformed by the node 100 and executes the various processes in thecommunication control method according to the embodiment. For example,the CPU 100 e executes each of the processing units illustrated in FIG.2 or each of the processing units illustrated in FIG. 5. Furthermore,the CPU 100 e reads and executes the program having the same function asthat performed by each of the processing units illustrated in FIG. 2 orFIG. 5 from the memory 100 d or the like so that the CPU 100 e canexecute the same function as that performed by each of the processingunits illustrated in FIG. 2 or FIG. 5.

According to an aspect of an embodiment of the wireless communicationmethod, the node, and the monitoring node disclosed in the presentinvention, an advantage is provided in that a separation location of anode can be specified.

All examples and conditional language recited herein are intended forpedagogical purposes of aiding the reader in understanding the inventionand the concepts contributed by the inventor to further the art, and arenot to be construed as limitations to such specifically recited examplesand conditions, nor does the organization of such examples in thespecification relate to a showing of the superiority and inferiority ofthe invention. Although the embodiments of the present invention havebeen described in detail, it should be understood that the variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A wireless communication method used in awireless system including a plurality of first nodes, a plurality ofsecond nodes and a third node which execute a wireless communicationusing a wireless ad hoc network, the wireless communication methodcomprising: selecting a selection node that is a send source of a packetwith the highest received radio wave intensity from among packets whichare transmitted by the plurality of second nodes, by the plurality offirst nodes; sending, to the selection node, a report packet thatincludes an identifier that specifies each of the plurality of firstnodes and whose destination is the third node, by the plurality of firstnodes; adding an identifier that specifies each of the plurality ofsecond nodes to the report packet which is received with the receivedradio wave intensity that is equal to or greater than a predeterminedvalue among the report packets which are transmitted by the plurality offirst nodes and relaying the report packet to the third node, by theplurality of second nodes; and detecting a node corresponding to theidentifier that is not included in the report packets received from theplurality of second nodes, by the third node.
 2. The wirelesscommunication method according to claim 1, wherein the sending includessending, when the report packet is sent to the third node, the reportpacket after adding, to the report packet, a combination of the receivedradio wave intensity and the identifier of the second node with areceived radio wave intensity that is equal to or greater than apredetermined value at the time when the packet is received, and thedetecting includes calculating the positional relationship or thedistance between the nodes by using the identifier of each of the nodesand the received radio wave intensity that are included in the receivedreport packet and by using the received radio wave intensity at the timewhen the report packet is received.
 3. The wireless communication methodaccording to claim 1, wherein the sending includes suppressing thereport packet from being created when the each of the plurality of firstnodes is a relay node that relays the report packet to another node inthe ad hoc network.
 4. A node comprising: a selecting unit that selects,from among packets received from neighboring nodes, a neighboring nodethat is a send source of a packet with the highest received radio waveintensity; a sending unit that sends, to the neighboring node selectedby the selecting unit, a report packet that includes an identifier forspecifying the node and whose destination is a monitoring node; and arelaying unit that adds an identifier of the node to the report packetthat is received from the neighboring node with the received radio waveintensity that is equal to or greater than a predetermined value andthat relays the report packet to the monitoring node.
 5. A monitoringnode comprising: a receiving unit that receives a report packet that issent from each node and to which an identifier for identifying a sendsource node of the report packet and an identifier of a node that relaysthe report packet are added in an order the report packet is relayed;and a detecting unit that detects a node that is not included in thereport packets received, from the nodes, by the receiving unit.